The present invention relates to devices for reading, by diascopy, an optical code carried by a disk or a transparent strip.
It is known that such a device comprises--in combination with a disk or strip comprising a succession of opaque zones and fine alternating transparent zones--a light source, a reticle or reading index, and a photo detector which detects if it is an opaque zone or a transparent zone which is in front of the reticle or the index, the source-reticle (or index)--photo detector assembly, on the one hand, and the disk or the strip on the other being moveable with respect to each other, either by rotation (case of the disk), or by translation (case of the strip).
Devices for reading an optical code by diascopy are described for example in U.S. Pat. Nos. 3,187,187 (Wingate), 4,182,953 (Hurley and Krystek) and 4,338,517 (Perrine).
Generally the disk or the strip is supported by a mechanical part whose angular position (case of the disk) or linear position (case of the strip) may be located whereas, in the reader properly speaking, the light source, the index (or the reticle) and the photodetector are perfectly aligned so as to define a specific optical path: the light emitted by the light source strikes the disk or strip shaped support in alternately opaque and transparent zones, while passing therethrough only if a transparent zone is opposite the index or reticle, which is generally formed by a narrow slit having advantageously the width of the transparent zones, and then striking the photo detector which emits an electric signal in response to the passage of each transparent zone in front of the index or reticle; this signal is amplified and shaped in an electronic unit associated with the photo detectors, before being counted or recorded for example.
When several reading tracks are provided on the disk or the strip, the reading device generally comprises as many source-index (or reticle)--photo detector (with associated electronic unit) assemblies as tracks, for example 10 such assemblies for a 10 bit coder.